1. Field of Invention
The invention relates to a fuel injection system for an internal combustion engine with a high-pressure pump for pumping the fuel into a high-pressure reservoir and with at least one injector connected to the high-pressure reservoir by a feed line. Operation of the fuel injector is controlled by a solenoid valve with fuel passages which are connected to the feed line, one of the fuel passages leads to an injection nozzle and another fuel passage leads to a control space which is delimited by a control piston interacting with a nozzle needle of the injection nozzle and which is connected to a low pressure return past a solenoid valve which controls the injector. Furthermore a pressure regulating valve is provided in the path of fuel flow between the high-pressure reservoir and the injection nozzle and has a passage used to direct fuel flow from the high-pressure reservoir to the injection nozzle.
2. Description of Related Art
DE 196 12 738 A1 has disclosed a fuel injection system of this general type with an injector controlled by a solenoid valve. The injector contains a pressure control valve which is combined with the control piston and controls the flow connection between the high-pressure reservoir and the injection nozzle in a manner dependent on the solenoid valve, such that the flow connection is interrupted between the injection processes but opened up during each injection process.
In this prior art embodiment, the fuel feed passage leading to the pressure space about the nozzle and needle valve is always connected to a restricted return line located on the low-pressure side. Before the start of an injection, only a very low pressure acts on the needle seat of the injection nozzle. As soon as the connection between the high-pressure reservoir and the needle seat is established, the pressure at the needle seat rises. Once the opening pressure of the injection nozzle is exceeded, injection starts. To end injection, the flow connection between the high-pressure reservoir and the needle seat is again closed and the pressure at the nozzle needle of the injection nozzle decreases rapidly. Once the pressure falls below the injector valve's opening pressure, the injection nozzle closes.
In reservoir-type injection systems of this kind, the operation of the nozzle needle is controlled in its stroke motion by fuel pressure. Accordingly, desirable subsequent post-injections, which contribute to reducing soot formation, are not readily carried out.